Sibling rivalry can start even before the birth of your new baby and last until four or five years of age. In fact, some forms of sibling rivalry may persist well into adulthood. Although this is normal, it can be disruptive.
You can help older children feel less jealous of their new baby brother or sister by...
praising them for their involvement in the baby's care (You will need to set clear rules about handling and picking up the new infant.)
making special efforts to spend time with the older sibling